Figure 5.
E. coli sepsis leads to long-term fibrosis. (A) E. coli sepsis induces decreased lung elasticity in baboon no. 2,509 that survived 27 months after experimental E. coli sepsis as compared with a group of five healthy control animals. This reflects a stiffer organ, as shown by the changes in lung compliance (C), expressed as the pressure difference between the interior of the alveoli (PA) and the pleural cavity (PPl) (transpulmonary pressure) required to affect a given change in the volume of air (ΔVL) in the lungs (C = ΔVL / Δ(PA-PPI). (B–D) Pseudocolor-encoded computerized tomography (CT) images of fibrotic lungs from the baboon that survived 27 months after experimental E. coli sepsis (B) as compared with a healthy control animal (C). Changes in mean gray values in 15 regions-of-interest from three representative CT scan images per experimental condition (fibrotic and control) are shown as a scatter plot (D). Data are presented as mean ± SEM (two-tailed Student’s t test; ***P < 0.001). (E–G) Staining with Mallory’s trichrome Masson (E; collagen in blue) or Sirius red (F and G; collagen appears as bright birefringent deposits under epipolarized light) detects extensive fibrosis within the lung parenchyma (F) of challenged baboons, as compared with healthy control animals (G). (H–J) Staining for procollagen 1 (H and I, red) and 3 (H and I, green), and matrix protein osteopontin (J) shows active collagen production and enhanced matrix deposition in the alveolar wall of challenged baboons. Procollagen production in healthy control animals is low and restricted to the adventitia of the large vessels (I, arrow) or airways (I, arrowhead). Nuclei are shown in blue. Overlay of green and red staining is shown as yellow. (K) Quantitative RT-PCR (qRT-PCR) of mRNA encoding the collagen 1α2 and collagen 3α1 chains shows strong increased production of these two major matrix proteins in the lung of sepsis survivors as compared with healthy control animals. Data are shown as fold ratio of challenged versus healthy control animals. (L and M) Biochemical determination of the collagen content of the lung using Sirius red (L), represented as percentage of total protein in lung homogenates, shows almost double-fold increase in the baboons that survived sepsis (n = 6) versus age matched control animals (n = 3). Procollagen 3 activation peptide levels are significantly increased in plasma of the six animals that survived sepsis for over 6 months (n = 6), as compared with the plasma of the same animals before experimental sepsis challenge (n = 6). Procollagen 3 levels in nonchallenged controls (9,989 ± 923 pg/ml, n = 3; not shown on the graph) were not statistically different from the prechallenge values of the experimental groups (10,025 ± 823 pg/ml, n = 6). Data are presented as mean ± SEM (two-tailed Student’s t test; ***P < 0.001. (N–P) Representative electron micrographs of the lung from an animal that survived sepsis challenge for 6 months (N and O) show extensive collagen (coll) deposition within the interalveolar walls as compared with a nonchallenged control animal (P). av, alveolae; RBC, red blood cells. Scale bars, 200 μm (E–G), 100 μm (H–J), 10 μm (N and O).